A radio frequency (RF) micro-electro-mechanical system (MEMS) provides lower power, higher performance, wider tuning range, and a freedom of integration which traditional RF components cannot. RF MEMS switches are basic building blocks for a variety of RF circuitry. These switches offer better RF performance, lower insertion loss and more isolation than their semiconductor counterparts such as field effect transistors (FETs) and PIN diodes. In addition, RF MEMS switches can operate at low power levels with a high degree of linearity and very low signal distortion. These features make RF MEMS switches very attractive for RF applications such as radar and communications. Indeed, RF MEMS circuits including variable capacitors, tunable filters, on-chip inductors and phase shifters built upon RF MEMS switches have demonstrated superiority over semiconductor devices.
RF MEMS switches can be classified into two types: resistive series and capacitive shunt switches. Both are typically fabricated on expensive semiconductor substrates such as gallium arsenide (GaAs), high-resistivity silicon, quartz or alumina due to the limitations of existing fabrication processes. The switches are then packaged and integrated into RF systems as discrete components since the substrates are generally incompatible with other RF elements. The discrete component packaging costs for RF MEMS switches are much higher than semiconductor switches and therefore, even though the fabrication cost of an individual switch is low due to batch processing, a discretely packaged RF MEMS switch component is expensive compared to the semiconductor switch alternatives.
Furthermore, the lack of a component-to-component compatible substrate typically requires the integration of all RF discrete components and circuits on a system module board. The RF MEMS switch, in addition to the other RF components such as antennas, phase delay lines and tunable filters, are attached and interconnected on the module board. The board-to-package external connections, as well as the switch-to-package connections internal to the RF MEMS switch add undesirable RF, capacitive and inductive effects which degrade system performance. As a result of these connections, the RF system requires additional matching circuits to reduce the unwanted signal reflections occurring as a result of unmatched connections. However, the matching circuits take up additional area and do not solve the matching problems entirely and also add cost and design overhead to the system.